Method and a device of treating a continuous material web with infrared light and heated air

ABSTRACT

A method and a device (1) to treat a paper web (12) by using air, which flows around and cools the infrared lamps (4), to impinge against the paper web and thereafter be removed. A glass plate (9), supported by a pair of glass holders (8), is used to shield the paper web from the infrared lamps. In order to improve the total efficiency and, in particularly, to achieve even and efficient drying of the paper web by using less energy, the cooling air outlets adjacent the glass holders are designed as adjustable width nozzles (19) to direct the heated air against the paper web. The nozzles extend across the entire width of the paper web and the cooling air is ejected from the nozzles at high speed thereby forming an air knife to tear apart the boundary layer of humid air which follows the paper web and subjects the paper web to a more intense heat treatment.

The present invention relates to a method of treating a continuousmaterial web, particularly a paper web, according to the preamble topatent claim 1. Also, the invention relates to a device designed tocarry out the method according to patent claim 1, which device isdefined in more detail in the first device claim.

When paper materials are dried, a continuous paper web is run past oneor several arrays of infrared heat elements. These elements compriseinfrared lamps, mounted in reflector frameworks and separated from thepaper web by means of glass plates in order to reduce the fire hazardand protect the lamps. Thus, the lamps must then be cooled and also theglass plates and the holders of the latter, because very hightemperatures are reached. In order to obtain such a cooling, the areabehind the reflector frameworks and their sheets as well as the glassholders is usually pressurized and the cooling air which is used isallowed through a system of cavities to flow past all the parts whichare to be cooled and finally to leave the heat elements and flow againstthe paper web, from which the air is sucked and possibly reused in thedrying process.

As to the above-mentioned conventional infrared heat elements thecooling air flows out usually through lines of holes or notaerodynamicly designed gaps across the web, which means that the coolingair is diffused very quickly close to the holes and reaches the paperweb with a comparatively low speed. The speed usually is so low, thatthe boundary layer of humid air along the paper web surface andfollowing it is not completely broken through. Consequently, the coolingair which flows against the paper web does not have a sufficient dryingaction, and thus several infrared heat elements are needed and/or anincreased radiation intensity and amount of supplied energy. Also, whenhole patterns are used, they may not cover the paper web evenly in theperpendicular direction, a streak effect and consequently an unevendrying effect being obtained. Also, the holes and the gaps respectivelycannot be adjusted and thus, the cooling air supply cannot be adjustedafterwards. The manufacturing and/or assembly costs can also betroublesome in conventional plants.

WO-A-87/005644 relates to an air-float drier, particularly for paperwebs, a number of units including ventilation and infrared heatradiation devices being mounted on alternately opposite sides of a webwhich is to be dried. By means of the ventilation equipment air jets aredirected substantially parallel to the web and the humid boundary layerof which consequently is not substantially influenced by the air jets,the main task of which is to bring about a pressurization in front ofthe infrared heat radiation equipment in order to bend the web away fromsaid equipment and support or stretch it in this way. As is realized,the entire drying device is very bulky and expensive as regards itsmanufacturing, assembly and operation, its energy consumption being verylarge. One of the drawbacks of the device as to its drying effect isalso that the ventilation air, which is supplied against the paper web,is not allowed to pass through the infrared heat radiation equipment tobecome heated there to an elevated and consequently drying-efficienttemperature but is circulated around said equipment, whereas the airwhich passes through said equipment is removed through cavities 23 and31 to be recirculated within the plant. The dimensions of the units arelarge and consequently the drying units of the entire assembly are verybulky, and how the ventilation air is taken care of is not discussed.

SE-B-404 213 relates to a device for drying a moving material webwithout a heat radiation equipment, the ventilation air being ejectedagainst the material web through a screen of holes, which have differentfimensions. It is true that the air is ejected perpendicularly to theweb surface, a continuous air-float effect being obtained, but the airstream unresiliently hits the boundary layer on the material web withoutbeing able to rip it open in any way. This drying device apparently isnot very efficient and useful in applications, in which a maximum dryingis to be accomplished within a minimum area, the supplied energy beingutilized in a maximum way.

SE-B-455 709 relates to a combined infrared radiation andventilation-drier, e.g. for paper webs. However, the ventilation air isnot directed against the web at all but is run parallel to it, noboundary layer-influence at all taking place. Of course, the drier inthis way has a strongly reduced efficiency and the energy consumption islarge without being of any sufficient service.

The object of the present invention is to as regards what has beendiscussed above improve and further develop the conventional methods anddevices for treating continuous material webs.

This object is achieved by carrying out a method of the type describedin the introductory portion above in accordance with the characterizingclause of patent claim 1. Also, said object is achieved by means of adevice according to the first device claim.

Additional characterizing features and advantages of the invention areset forth in the following description, reference being made to theaccompanying drawings showing a preferred but not limiting embodimentand in which:

FIG. 1 shows a device according to the invention in a vertical sectionalview;

FIG. 2 is a view along line A--A in FIG. 1;

FIG. 3 shows a detail according to FIG. 1 having a completely opendamper;

FIG. 4 shows various views of a glass holder according to the invention;and

FIG. 5 is a view of one part of the glass holder shown in FIG. 4.

In the drawings a device 1 according to the invention is shown in itsentirety. It comprises a reflector framework with reflector sheets 3 andinfrared lamps 4. The frameworks are suspended in mounting means 5. Inconnection with the frameworks there preferably are exhaust air ducts 6adjacent the two ends, through which ducts the predominant portion ofthe intake air, ejected towards the paper web, is removed, e.g. by meansof negative pressure, not shown in detail. The intake air can besupplied by a fan, not shown, and flow through said frameworks in a wayknown per se and not shown in detail here.

Glass holders 8 are mounted below said mounting means 5, e.g. screwed onby means of screws 7 and in pairs support glass plates 9, which areinserted into grooves 10 in a lower holder part 11, which suitably isdesigned as a flat member, which extends in a plane parallel to and at adistance above a passing paper web 12. The two longitudinal sides of thelist suitably are bevelled below and/or above the plane of the glassplates.

Glass holder part 11 suitably is made integral with e.g. two spacers 13,mounted at a distance from each other, and with a guide part 14 mountedabove them, which latter is plate-shaped with an outer longer side,which is smoothly bent downwards towards the paper web and thus forms aguided flange 15. Different thicknesses of material can be used alongthe cross-section of the entire guided part, the flange e.g. beingconsiderably thinner. Guide part 14 without its guide flange extends atleast approximately in a plane-parallel direction in relation to holderpart 11. A minor convergence can possibly be used towards the flange atthe inner half of guide part 14.

The fastening screws of the glass holders suitably extend through holes16, which extend in a central direction through spacers 13 and theadjacent areas of parts 11 and 14.

There is also a groove 17 in the outwardly turned long edge of parts 11,which groove is designed to suitably displaceably in the longitudinaldirection of the paper web receive a damper 18, which is a flat member21 with the exception of the outer long edge, namely the edge facingflange 15, which suitably is thick and forms one side of a nozzle gap19, the other side of which is formed by stationary flange 15. Said oneside is a damper surface 20 having a plane which is parallell to flange15 and suitably extends on the two sides of the plane, e.g. a centerplane formed by said flat member 21. In connection with itsplane-parallel extension surface 20 continues in a lower and an upperbend and the upper bend radius may be twice as large as the lower one.The bends are approximately half circular-cylindrical in such a way,that above member 21 a twice as wide and/or thick guide bead 22 isobtained as compared to a guide bead below member 21. Thanks to thedescribed design of the damper an efficient cooling air flow is obtainedat the inlet of the nozzle as well as at its outlet.

As is shown in the drawings the damper can be adjusted into variouspositions by inserting it into groove 17 to different depths and lockedin these positions by means of screws 23 fastened in list 11. In thisway a nozzle gap 24, formed by flange 15 and surface 20, is adjustedsteplessly with a great accuracy. The free long edge of the flange canthus advantageously end approximately in front of the central part ofsurface 20 as regards its extension in a transversal direction inrelation to the paper web. Flange 15 is in its turn suitably positionedin front of the center of the corresponding exhaust air duct 6 asregards its extension in the longitudinal direction of the paper web.The gap width can be e.g. 4-11 mm and as large as 16 mm without thedamper.

Flat member 21 is provided with holes 25, adjacent its ends and oblongin the displacement direction of the member and designed to surroundscrews 23. Between holes 25 there are recesses 26 in the flat list aboutspacers 13. Guide part 14 is on its free side provided withlongitudinally through locating ribs 27, which have a trapezoidalprofile, at either side of spacers 13 in order to hold and be positionedon raised portions 28, which extend downwards from the ends of eachunit 1. Also, guide part 14 is provided with holes 29 and 30, designedto render possible and facilitate respectively an assembly anddisassembly work.

Since, as is shown in the drawing, a series of devices according to theinvention can be joined to each other in order to bridge the whole widthof the paper web, the mutually adjacent device edges preferably beingoblique, an uninterrupted gap is obtained and consequently a streaklesstreatment of the paper web as to heat treatment as well as to coolingair supply. The last mentioned supply has never before been supposed toalso result in a treatment but merely as a certain ejection zone forconsumed cooling air. Thanks to the characterizing features of thepresent invention, also the feature that the cooling air can be stronglypressurized and consequently can have a high ejection speed through thenozzles, it is possible to transform the consumed cooling air, which infact is a strongly heated exhaust air, to an air-knife, which extendsacross all the width of the paper web and with a speed of up to 70m/sec. flows towards the paper web and efficiently penetrates theabove-described boundary layer along the paper web and rips open thislayer adjacent the inlet to the first nozzle. In connection with this aforced drying-process can take place, since said boundary layer, whichhas been ripped open, now has a strongly reduced moisture content andabsorbs less heat radiation as well as does not have a restrainingeffect on the moisture disappearance from the paper web any longer. Theremaining parts of the boundary layer which has been ripped open aresubsequently attacked on the downstream side of the second nozzle andalso in this area takes place a more efficient vacuum removal of a majorboundary layer portion in the exhaust air than what has been the casebefore, which also results in a forced drying downstreams of theIR-equipment.

The glass plates can form a closed unit across the width of the paperweb, which does not allow exhaust air to flow through it, or a certainadvantageous exhaust air discharge can take place, e.g. due to a mutualoverlapping of the glass plates in a known way, which allows a smallamount of air to flow through the overlapping zones. Such a limitedoutflow may contribute to the advantageous total efficiency of thedevice, i.a. due to an improved cleaning of said glass surfaces.

The characterizing features of the invention are: The designed nozzle(the gap) can be adjusted in a simple fashion to the desired outflowspeed in order to meet the requirements of different paper webs. Avarying and adjustable outflow speed and a pressure impulse causedthereby against the paper web on the air supply side can in combinationwith a constant vacuum removal of exhaust air, integrated in theIR-housing, across the width of the web allow the IR-housing to functione.g. as a guide roller regarding the web having an arbitary bendingdirection. Thus, by adjusting the nozzles of the glass holders withdifferent gap widths across the web different speeds/pressure impulsestowards the web for different web sections can be obtained, a positiveactuation of the runnability of the paper web being attained, since theIR-housing then functions as a guide roller.

The nozzle is to be designed aerodynamicly in a proper way, in order todevelop a satisfactory collected air stream, the maximum velocity ofimpact of the air against the paper web being insignificantly lower thanthe outlet-speed, also at a distance of 30-40 mm. If the outlet openinge.g. has sharp edges, turbulences and significant speed reductions areobtained.

The dimensions of the nozzle jointly with the overlapping of the glassplates can result in a pressurization under the plates with outletspeeds of up to 70 m/s and simultaneously a most efficient perpendicularimpact blowing is used against the paper web in order to achieve amaximum convection heat transmission and boundary layer effect. Theelevated outlet speed, almost twice as large as in conventional systemsallows, jointly with the more collected air flow, a considerablyimproved drying effect, particularly pronounced in IR-positions with ahigh moisture content in the paper web.

The gap design of the glass holder allows, jointly with the position ofthe exhaust air duct, placed at a lower level, a maximum portion of theair supplied to the web to be captured and reused in other suitabledrying sections in the process.

The adjustable gap width of the glass holders allows the impact flowspeed against the paper web to be varied in a simple way in an IR-deviceto a suitable level for freely running paper webs having a low webtension. It is in this way possible to use the highest suitable supplyair speed considering the runnability of each individual paper web andthe need of influencing the boundary layer in connection with thedrying.

The individual adjustable gap width and then also the impact blow speed,the pressure impulse of each module in the cross-direction of the weballows, jointly with an air exhausting device, mounted across the weband integrated in the IR-housing, i.e. the space above or behind theframeworks, an adjustment of a freely running web having a varying webtension/web handling in the transversal direction, which results in animproved runnability for the web and consequently a reduced web breakfrequency. A special case of this is the possibility described above to,by means of the guidable pressure impulses of the glass holderstransversely to the web allow the IR-housing to function e.g. as a guideroller having a selectable bend direction regarding the web. In thisconnection it is important to take into consideration also the tensioneffect, which is obtained due to the suction zones 6 in connection withevery blowing gap. A sufficiently large suction force, which is obtainedthrough a corresponding negative pressure in suction ducts 6 will resultin a certain web tension before and after each unit 1, positivelycounteracting and stabilizing the tensioning, which is obtained by meansof said air-knives. Since it is easy and simple in a device according tothe present invention to steplessly adjust the air supply and theexhaust air amounts as well as the gap width, in this way an excellentinstrument is obtained designed to solve e.g. stabilization and breakproblems of a freely running material web, also in case such a web has avery low surface weight, e.g. about 30 g/m² and/or a high speed, e.g.about 1000 m/min.

What is claimed is:
 1. A heating and ventilation unit for treating acontinuous web of material, said unit comprising a housing being open atone end thereof and defining a hollow interior chamber therein, an arrayof infrared lamps (4) being supported in the chamber proximate to andfacing toward the open end of said housing, a pair of glass holders (8)being attached along opposite longitudinal edges of the open end of saidhousing, a glass plate (9) being supported by said pair of glass holdersand extending substantially across the width of the open end, means forproviding a flow of cooling air to said housing for cooling said lamps,at least one spacer (13) separating each said pair of glass holders fromthe longitudinal edges of said housing thereby to define an elongateclearance between each longitudinal edge of said housing and theadjacent glass holder (8), an air flow guide flange (14) attached toeach said longitudinal edge of said housing and extending in a planeparallel to said glass plate, each said air flow guide flange (14)having a remote end curving back toward said glass plate holder andterminating in an end portion (15), each said end portion (15) and theadjacent glass holder (8) defining a nozzle gap (19, 24) therebetweenextending the entire length of said housing, whereby in use cooling air,supplied by said means for providing cooling air, passes around andcools the lamps (4) and becomes heated, and the heated air exits saidhousing through the clearances and is directed by the guide flanges (14,15) through said nozzle gaps (19, 24) to form air knives extendingacross the longitudinal length of the open end and directedsubstantially at a right angle relative to said glass plate.
 2. Aheating and ventilation unit according to claim 1, wherein said meansfor providing a flow of cooling air and said nozzle gaps (19, 24)provide the air knives with a velocity of up to 70 m/sec.
 3. An heatingand ventilation unit according to claim 11, in combination with aplurality of other units each comprising a housing being open at one endthereof and defining a hollow interior chamber therein, an array ofinfrared lamps (4) being supported in the chamber proximate to andfacing toward the open end of said housing, a pair of glass holders (8)being attached along opposite longitudinal edges of the open end of saidhousing, a glass plate (9) being supported by said pair of glass holdersand extending substantially across the width of the open end, means forproviding a flow of cooling air to said housing for cooling said lamps,at least one spacer (13) separating each said pair of glass holders fromthe longitudinal edges of said housing thereby to define an elongateclearance between each longitudinal edge of said housing and theadjacent glass holder (8), an air flow guide flange (14) attached toeach said longitudinal edge of said housing and extending in a planeparallel to said glass plate, each said air flow guide flange (14)having a remote end curving back toward said glass plate holder andterminating in an end portion (15), each said end portion (15) and theadjacent glass holder (8) defining a nozzle gap (19, 24) therebetweenextending the entire length of said housing, whereby in use cooling air,supplied by said means for providing cooling air, passes around andcools the lamps (4) and becomes heated, and the heated air exits saidhousing through the clearances and is directed by the guide flanges (14,15) through said nozzle gaps (19, 24) to form air knives extendingacross the longitudinal length of the open end and directedsubstantially at a right angle relative to said glass plate; andtheplurality of other units being arranged in series with the air knivespositioned in an end to end relationship such that the air knives formtwo continuous elongate air knifes which span the entire width of a webto be dried.
 4. A heating and ventilation unit according to claim 1,wherein said unit further comprises at least one vacuum duct (6) locatedon each sides of said housing adjacent the air flow guide flange (14)for removing the air which exits the nozzle gap (19, 24) after treatinga web.
 5. A heating and ventilation unit according to claim 1, whereinsaid unit further comprises a reflector framework (2) mounted adjacentthe lamps, remote from said glass plate (9), to reflect radiation fromthe lamps (4) through said glass plate (9).
 6. A heating and ventilationunit according to claim 1, wherein said pair of glass holders (8) areintegrally formed with at least two said spacers (13), mounting holesextend through each of said pair of glass holders (8) and through saidat least two spacers, and threaded bolts (23) engage with the mountingholes and with mountings holes provided in said housing to attach saidpair of glass holders (8) to said housing.
 7. A heating and ventilationunit according to claim 1, wherein each said glass holder (8) has alongitudinally extending groove (17) provided in a side thereof remotefrom the open end, a planar inner portion (21) of an elongate damper(18) is received in each said groove and an outer portion of said damperextends from said groove and terminates in an outer end portion thatcooperates with the flange (14, 15) to define said nozzle gap (19).
 8. Aheating and ventilation unit according to claim 7, wherein said outerportion of each said damper has a thickness that is greater than that ofthe inner planar portion and has a planar outer surface (20) whichextends substantially perpendicular to said glass plate andsubstantially parallel to the end portion (15) of the guide flange (14),and opposed longitudinally edges of the end surface (20) are curved backtoward the inner portion (21) of the damper and thereby define a pair ofopposed longitudinally extending hemi-cylindrical beads (18, 22).
 9. Aheating and ventilation unit according to claim 8, wherein thehemi-cylindrical bead (22) located proximate to the open end has aradius that is about twice as large as the hemi-cylindrical bead (18)remote from the open end.
 10. A heating and ventilation unit accordingto claim 7, wherein said pair of glass holders (8) are integrally formedwith at least two said spacers (13), mounting holes extend through eachof said pair of glass holders (8) and through said at least two spacers,each said damper (18) has two transverse slots (25) extendingtherethrough, and threaded bolts (23) engage with the mounting holes andsaid transverse slots (25) to secure said pair of glass holders (8) andsaid dampers to said housing via threaded holes provided in saidhousing.
 11. A heating and ventilation unit according to claim 10,whereby the transverse slots (25) are sized and positioned such that thedampers (18) may be adjusted at an angle so that said nozzle gap has anincreasing width along the length of said unit.
 12. A heating andventilation unit according to claim 10, wherein said transverse slots(25) are sufficiently long such that the nozzle gaps are adjustable to awidth of from about 4 mm. to about 11 mm.
 13. A heating and ventilationunit according to claim 10, wherein the guide flanges (14, 15) areintegrally formed with the spacers (13) and extend from a side of thespacers remote from said open end.
 14. A method of treating a continuousweb of material by providing a unit for treating a continuous web ofmaterial, said method comprising the steps of:using a housing which isopened at one end thereof and defines a hollow interior chamber therein;supporting an array of infrared lamps (4) in the chamber proximate toand facing toward the open end of said housing; attaching a pair ofglass holders (8) along opposite longitudinal edges of the open end ofsaid housing; supporting a glass plate (9), by said pair of glassholders, which extends substantially across the width of the open end;separating each said pair of glass holders from the longitudinal edgesof said housing with at least one spacer (13) thereby to define anelongate clearance between each longitudinal edge of said housing andthe adjacent glass holder (8); providing an air flow guide flange (14)which extends from each said longitudinal edge of said housing in aplane parallel to said glass plate, each said air flow guide flange (14)having a remote end curving back toward said glass plate holder andterminating in an end portion (15); defining a nozzle gap (19, 24),extending the entire width of the web to be dried (12), between eachsaid end portion (15) and the adjacent glass holder (8); supplyingcooling air to said housing which passes around and cools the lamps (4)and becomes heated; exhausting said heated air from said housing throughthe clearances; and directing said heated air, via the guide flanges(14, 15), through said nozzle gaps (19, 24) to form air knives extendingacross the longitudinal length of the open end and directedsubstantially at a right angle relative to said glass plate.